Dynamics of the sulphate aerosol size distribution on a global scale

摘要

Parameterizations for size-dependent aerosols have been implemented in the Canadian Centre for Climate Modelling and Analysis (CCCma) atmospheric general circulation model (AGCM). This new model version considers comprehensive physical and chemical processes that are associated with the sulphate aerosol size distribution, including nucleation, condensation, hygroscopic growth, aqueous-phase chemistry, and dry and wet deposition. Results from in situ surface and airborne observations and remote sensing were used to validate the model. The comparisons give evidence for realistic sulphate size distributions over the regions where sulphate is the dominant aerosol type. In agreement with earlier published studies, it is found in sensitivity tests that the global sulphate burden is predominantly affected by wet deposition. However, the mass size distribution is mainly affected by coagulation, condensation, and below-cloud scavenging on the global scale. There is only weak sensitivity of the simulated mass size distribution to changes in in-cloud oxidation and the efficiency of nucleation. It is shown that the low sensitivities are caused by a compensating effect of coagulation in the former and low sensitivity of the mass size distribution to changes in nucleation rate and condensation efficiency for the latter case.